Linear motionBiomechanics of movement
The human body, like any other body, will only begin to move or, if is already moving, change its speed or direction, when the resultant force acting on it (the resultant of all the external forces acting on it) becomes greater than zero. Furthermore, the amount of change in speed or direction that occurs will depend upon the magnitude and direction of the resultant force, i.e. there is a direct relationship between change of resultant force and change in movement. Isaac Newton (1642-1727) described this relationship in what have come to be known as Newton’s laws of motion. In addition to the three laws of motion, Newton’s law of gravitation describes the naturally occurring force of attraction that is always present between any two bodies. A body falls to the ground because of the gravitational attraction between the body and the earth and the planets are maintained in their orbits round the sun by the gravitational attraction between the planets and the sun. The purpose of this chapter is to introduce the fundamental mechanical concepts underlying the study of linear motion, in particular, Newton’s laws of motion and gravitation.